1. Field of the Invention
The present invention generally relates to connectors. In particular, various embodiments of the present invention concern a shear bolt with a safety feature to prevent accidental dropping of the sheared bolt head.
2. Description of the Related Art
Various situations arise in which the use of a shear bolt is desirable to ensure that a bolted connection is torqued to the proper value. A shear bolt comprises an extended torque head portion that is designed and constructed to shear off the main body of the bolt at a predetermined torque. Such bolts are described, for example, in U.S. Pat. No. 6,884,124 to Douglas Craig, entitled “Obstruction Assembly for Use with Disconnectable Joints and Methods of Using the Same,” the contents of which are incorporated herein by reference.
As illustrated in FIG. 1, a conventional shear bolt 100 comprises a torque head portion 110, which protrudes from a main bolt portion 150 by a predetermined distance. Main bolt portion 150 has the appearance of a standard bolt and includes a head portion 151 with a threaded, or partially threaded, shaft portion 152. The head portion 151 and shaft portion 152 are generally designed to have dimensions similar to those required of the standard (i.e., non-shear) bolt for the same application. Hence, while main bolt portion 150 may have the same length as the standard bolt for the application, shear bolt 100 may have an overall longer length than such standard bolt. The shear bolt 100 is preferably formed as a single, integrated piece, although it is also possible to join torque head portion 110 and main bolt portion 150 together as respective separate pieces to form the integrated shear bolt 100.
Torque head portion 110 of shear bolt 100 typically includes an extended head portion 111 and a stem portion 112. Extended head portion 111 and stem portion 112 are generally formed as a single integrated piece, although they could also be formed as separate pieces that are rejoined together. Stem portion 112 extends from surface 153 of head portion 151 of main bolt portion 150 to the underside of extended head portion 111. Stem portion 112 is designed such that the extended head portion 111 of shear bolt 100 will break off from the main bolt portion 150 when a pre-determined amount of torque is applied to the extended head portion 111. A shear location 113 of stem portion 112 may be at any desired location, such that stem portion 112 may remain fully attached to extended head portion 111, to main bolt portion 150, or partially attached to either or both, as a matter of application-specific design choice.
Stem portion 112 is typically constructed and designed to have a thinner width than the width of shaft portion 152 of main bolt portion 150, and is designed to shear off at shear location 113 at a pre-determined torque value, such as between approximately 50 to 60 foot-pounds of torque. Extended head portion 111 can comprise a hexagonal shape and the upper surface of extended head portion 111 can be flat, making it suitable for tightening or loosening using conventional tools. The width of extended head portion 111 can be greater, equal to, or smaller than the width of head portion 151.
Shear bolt 100 can be used in situations, for example, in which assurance is required that main bolt portion 150 has been tightened to the proper, pre-determined, torque. For example, the extended head portion 111, due to its excessive length, may prevent further steps in an installation process from being possible, such as the mounting of a sleeve over main bolt 150, until the extended head portion 111 has been removed, thus requiring that the extended head portion 111 be sheared off before the installation can be finished, and thus ensuring that main bolt 150 has been tightened to the proper torque value.
Shear bolt 100 may be used in situations in which extended head portion 111 may fall from some height when sheared off from head portion 151. For example, shear bolt 100 can be used by electric utilities to connect two cables together. Typically, the cables are overhead and affixed to insulators that are mounted onto utility poles. Use of shear bolt 100 ensures that the connection is torqued to its proper value. However, since extended head portion 111 is free after installation, it is possible for extended head portion 111 to fall from the mechanic's hand and damage property or injure individuals at ground level. This is especially true since mechanics may be required to wear heavy gloves during work on energized cables, thus making it difficult to hold onto components.
It is therefore desirable to provide a shear bolt that can avoid inadvertent dropping of the sheared bolt head during installation.